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Brake Fluid Flushing-A Needed Service?
I try to flush my brake system once per year. This
means replacing your old fluid with new. I use a
bladder-equipped (keeps air separate from the brake
fluid so that brakes aren't dangerously "spongey")
pressure bleeder with individual fitting for my
vehicle. Some cars need a special device to flush
the ABS system section during this operation. This
operation has really reduced wheel cylinder/master
cylinder repairs on my vehicles over the years,
and the brakes seem to operate better, as well. I'm
in real estate sales, and do a lot of short-haul,
stop-and-go driving. You all should see the color
of the fluid if you go, say, longer than 2 years
between flushing. The DOT 3/4 (glycol based) fluids
tend to attract moisture, and tend to thus boil at
a lower temperature--causing possible braking
problems or failure when under severe use, e.g.,
down a steep grade, etc--corrode surfaces they
contact(important-can seriously "pit"/damage master
and wheel cylinders!) when moisture-laden; also
seriously damage painted surfaces they might drip
on. I understand that for perhaps $20 or less per
car, manufacturers could use silicone-based brake
fluid systems, which attract less moisture, are
less corrosive, less damaging to paint, boil at a
much higher temperature (safer in heavy braking
situations). The bottom line: there would be
likely longer-lasting vehicles, fewer repairs,
fewer accidents, and quite likely many, many, many
dollars saved in many ways. Why don't we demand
that this be done!!!?? I'd pay the extra $$,
wouldn't you?
boomer18
means replacing your old fluid with new. I use a
bladder-equipped (keeps air separate from the brake
fluid so that brakes aren't dangerously "spongey")
pressure bleeder with individual fitting for my
vehicle. Some cars need a special device to flush
the ABS system section during this operation. This
operation has really reduced wheel cylinder/master
cylinder repairs on my vehicles over the years,
and the brakes seem to operate better, as well. I'm
in real estate sales, and do a lot of short-haul,
stop-and-go driving. You all should see the color
of the fluid if you go, say, longer than 2 years
between flushing. The DOT 3/4 (glycol based) fluids
tend to attract moisture, and tend to thus boil at
a lower temperature--causing possible braking
problems or failure when under severe use, e.g.,
down a steep grade, etc--corrode surfaces they
contact(important-can seriously "pit"/damage master
and wheel cylinders!) when moisture-laden; also
seriously damage painted surfaces they might drip
on. I understand that for perhaps $20 or less per
car, manufacturers could use silicone-based brake
fluid systems, which attract less moisture, are
less corrosive, less damaging to paint, boil at a
much higher temperature (safer in heavy braking
situations). The bottom line: there would be
likely longer-lasting vehicles, fewer repairs,
fewer accidents, and quite likely many, many, many
dollars saved in many ways. Why don't we demand
that this be done!!!?? I'd pay the extra $$,
wouldn't you?
boomer18
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Comments
Also, my understanding is that rubber parts in most all stock brake sytems are the "seal swell" type and thus incompatible with silicone fluid-those rubber parts would need to be replaced with appropriate ones before using silicone fluid. This is another reason that mfrs would not recommend silicone fluid in basically all stock brake systems. I hadn't seen information on silicone fluid aeration! Maybe it's time to develop another fluid altogether!
What do you think about periodic flushing of brake fluid?
boomer18
Just make certain to not let air back into the piston-use a big C clamp to push the piston in-easier than prying it back.
I read or heard somewhere from a mechanic that your method, common practice before, could possibly damage the newer(ABS?) systems by forcing debris back up the lines. Has anyone else heard something on this?
'Forgot to thank you for pointing out that fluids from car maintenance should be properly collected/disposed of!!!!! In the San Gabriel Valley area of Southern California, we have regular hazardous waste "round-ups" in various locations, as well as hotlines for such info in between events. Hopefully we can move toward an even better set-up for such disposal, so that the inconvenience involved doesn't lead to more poisoning of people and things.
Some people used to use the C clamp to push the fluid back into the brake system-sometimes causing the master cylinder to overflow. The real danger is getting air into the system-you can buy or make a device to keep air out of the system-use a small glass jar, 3/8" id clear flexible hose, fill it with fluid, fluid in jar covering end of the line and this will keep air out of the system. In my experience it is only necessary to do this when replacing the caliper and filling an empty disk brake piston.
First, it should be understood that water will probably eventually find it's way into any brake hydraulic system through microscopic pores in flex hoses and master cylinder reservoir diaphragms, at the rate of 2-3% annually. Glycol fluids are hygroscopic (they absorb moisture) for a reason. Any moisture contamination in the system will tend to be dispersed throughout the system, minimizing water concentration at any specific location.
Silicone fluids, being non-hygroscopic, will not disperse water, which can cause high concentrations of water at the lowest points of the system such as the brake calipers or low points in lines (water is heavier than silicone fluid and will collect at the low points). This presents 2 problems: localized higher corrosion rates; and more chance of water collecting and boiling in the calipers under heavy braking, causing gassing and pedal fade. Silicone fluids also contain about 3X as much dissolved air as glycol fluids and are about 2X more compressible, which may cause the characteristic spongy pedal feel associated with their use, cause aeration when forced through small orifices, and make bleeding more difficult.
Regarding seal swelling, some early silicone formulations had an incompatibility problem with glycol-designed seals but that has been corrected in most current formulations. If glycol-designed seals were designed to swell with use, then every rebuilt caliper/wheel cylinder would leak when first installed.
Currently, Harley Davidson is the only U.S. manufacturer to specify silicone fluid, and that's for paint damage concerns. None recommend silicone fluid in ABS equipped vehicles.
FLUID TYPE DRY - boiling point - WET
@ 3% water
DOT 3 glycol 401 F 284 F
DOT 4 glycol 446 F 311 F
DOT 5 silicone 500 F (humidified)=356 F
DOT 5.1 glycol 518 F 375 F
DOT 3 represents the MINIMUM standard for disc brake fluid boiling points. I recommend Valvoline SynPower @ 513 F & 333 F, and Ford Heavy Duty glycol fluids to my customers.
For anyone still wanting to switch from glycol to silicone fluid, be advised that the two do not mix, and will cause coagulation. The system must first be thoroughly flushed with denatured alcohol or methyl hydrate.
The bottom line is simple. Any brake hydraulic system is subject to water contamination. Glycol filled systems should be flushed every 2-3 years (this is an issue of time and relative humidity, not accumulated mileage). Silicone filled systems should be flushed annually.
Sorry for the textbook, folks, but there it is.